It is planned to study the following specific aspects of the male reproductive function: l. Role of the epididymis on sperm maturation: a. Hormonal control of sperm maturation; b. In vitro sperm maturation; c. Biochemical changes in sperm concomitant with maturation. 2. Role of the epididymis on sperm resorption. Bibliographic references: Danzo, B.J., Eller, B.C., Judy, L.A., Trautman, J.R., and Orgebin-Crist, M.-C. Estradiol Binding in Cytosol from Epididymides of Immature Rabbits. Molec. Cell. Endocr. 2: 91- 105,1975; Danzo, B.J., Eller, B.C., Orgebin-Crist, M.-C., and Cooper, T.G. Effects of Efferent Duct Ligation on 5 alpha-Dihydrotestosterone Binding and Sperm Maturation. In: Control of Male Fertility, John J. Sciarra, Colin Markland, and J. Joseph Speidel, Eds., Harper & Row, Hagerstown, Maryland, pp. 89-96, 1975.